1. Field of the Invention
The present invention relates to a method for producing a ruthenium complex including a carboxylate and an optically active bisphosphine as ligands (hereinafter, referred to as a carboxylate complex).
2. Brief Description of the Related Art
Carboxylate complexes are known to be a useful catalyst in asymmetric hydrogenation reactions. As the production methods thereof, the following methods are known, for example. In method (i), Ru2Cl4(Lig)2(NEt3) produced from [RuCl2(cod)]n, a phosphine ligand (Lig) and triethylamine under reflux in toluene overnight is reacted with a carboxylate salt in an alcohol solvent such as methanol, ethanol and t-butanol, at 20° C. to 110° C, the solvent is evaporated to dryness; and the complex is extracted with an alcohol solvent (U.S. Pat. No. 4,739,084). In method (ii), RuCl2(binap)(dmf)n synthesized by stirring [RuCl2(benzene)]2 and BINAP in a DMF solvent at 100° C. for 10 minutes is transferred to a separately-prepared solution of sodium acetate in methanol under an argon flow, the solution is stirred vigorously, degassed toluene and water are repeatedly added to wash the solution, the solution is concentrated to dryness, and the complex is recrystallized from toluene/hexane (J. Org. Chem., 57, 4053 (1992)). In method (iii), [Ru(p-cymene)(OAc)2] obtained by reacting [RuCl2(p-cymene)]2 with a large excess of silver acetate in toluene is reacted with MeO-BIHEP in methylene chloride at 50° C. for 48 hours (U.S. Pat. No. 5,488,172).
However, in the conventional method (i), after the reflux in toluene overnight, the evaporation to dryness and solvent replacement have to be performed. Moreover, the resultant complex hardly has a uniform structure, and 40 equivalent of sodium acetate is used to convert the complex to a carboxylate complex. Furthermore, in order to produce a synthetic intermediate of the carboxylate complex, triethylamine, which is not needed in the end, needs to be added, and accordingly the method (i) is also disadvantageous in cost. In the method (ii), the condition in the DMF solvent at 100° C. for 10 minutes is unrealistic in industrial-scale production. Besides, since the reaction takes place at high temperature, the decomposition of the complex or the like is highly likely to occur. Moreover, as the procedure further proceeds, the solvents are added sequentially, and accordingly 100 equivalent volumes of the solvents are needed with respect to the target complex. The method (iii) has difficulties because [Ru(p-cymene)(OAc)2] is a deliquescent and hard-to-handle intermediate, and the use of expensive silver acetate causes a cost problem, also. As described above, these conventional techniques have the following problem in common: the operations are complicated, and thus the production of by-products, the decomposition of the complexes and the like occur, in producing the carboxylate complexes. Accordingly, the reduction in yield, purity and the like is inevitable.